Metabolic Rate System


I’ve been wondering a lot about the transition from microscopic to macroscopic, and how we will design gameplay as an early 3D organism. We have a very good understanding of what Microscopic organisms function like, but the concept for Macroscopic organisms is more murky. We have vague ideas like that we want the player to be able to place organs like hearts, lungs, stomachs, etcetera. But this raises so many questions:

  • What do these organs do?
  • How do they work together?
  • Can an organism evolve the highest level heart possible without ever evolving a lung?
  • And how do we make it possible for simple organisms to not even have a heart? Or not even have a stomach?
  • And how do we design this in such a way that it feels like a natural continuation from what you played through during microscopic gameplay?

I recently came up with an idea to address all of this called the Metabolic Rate System. I would usually keep this in my notes and save it for later when this topic comes up, but I feel like it actually ties into some gameplay features we have planned (such as the Diffusion Rate trait I’ve discussed before). So I want to bring it up, explain what I think makes it worthwhile, and how it would impact our future game design if accepted.


There will be a new trait called Metabolic Rate. This represents the total amount of energy that the organism can produce in any given second. Think of the organism like a power plant, and their Metabolic Rate is the total electricity they can produce per second. Metabolic Rate will be used to determine a creature’s top speed, strength, stamina, and many other variables. It will almost be like ATP in the microscopic stages.

However, for a creature to produce energy, they must consume food, water, and gas. So we will add in traits like Circulation Rate (the rate at which gas is circulated to the tissues), Hydration Rate (the rate at which water is absorbed by the creature) and Digestion Rate (already exists. The rate at which food is absorbed by the creature). ALL THREE of these rates will be needed to maintain a creature’s metabolism, therefore the Metabolic Rate will be calculated as the LOWEST of these three rates of a creature.

One extra layer: Digestion Rate and Circulation Rate will both depend on another rate themselves. Ingestion Rate will represent how quickly an organism can consume food, which is then passed over to digestion. Respiration Rate determines how quickly an organism can absorb gas, which is then passed over to the blood for circulation. Both Digestion Rate and Circulation Rate will be limited by Ingestion Rate and Respiration Rate, respectively.

Therefore, the final chart comes out to be:

If any of these three components of the Metabolic Rate ceases, an organism will begin to die. Therefore, a creature can die of dehydration (Hydration Rate at 0), starvation (Digestion Rate at 0), or suffocation (Circulation Rate at 0).

A creature can of course stock up on a certain resource so that they do not need to constantly produce it. A filter feeder may constantly be ingesting food, but a predator may have an irregular eating pattern. Instead it does not eat for a while, then catches a big prey which lets him consume a lot of food all at once and store it, slowly digesting it and feeding its metabolism until he can find his next prey.

This system is also very flexible to different metabolisms. The metabolism of a creature defines what rate it needs of each component. Some creatures may not need to eat at all, surviving purely off of water and gas. Some creatures may survive on a different fluid than water, but we will still refer to it as hydration. Different foods (plants, meat, inorganic material) will all fall under food that is consumed under the Digestion Rate component.


  • It gives a function for the many different digestive, circulatory, and respiratory organs we want the player to be able to place in the Organism Editor.
  • In nature, the digestive, circulatory, and respiratory systems are highly linked. This is the only realistic way I can think of of tying all three systems together. A name I’ve seen mentioned is the “Gastrovascular System” to refer to these three systems working together.
  • It creates natural bottle-necks that means that you can’t evolve one part of your Gastrovascular System too far without making sure other parts are appropriately evolved. For example, a larger heart is useless if you cannot feed it with more gas, which may require you to first evolve gills before you grow your heart. Perhaps a small aquatic creature has no problems with hydration and circulation, so if he wants to increase his metabolism only digestive system mutations would be useful. This is actually very realistic, as when we look at nature we see that species have always had to evolve their Gastrovascular System in this stepwise process.
  • It ties in well with the Microbe Stage. Diffusion Rate is already a trait I’ve suggested before that should be added, AKA a variable rate at which a cell can absorb compounds from the environment. This would effectively be the Respiration Rate.
  • Because multicellular life starts simple and underwater, most of this chart would not apply at first. Hydration Rate would always be filled because the creature would be surrounded by water which will constantly flow into their organs via their skin (until they evolve thicker skin that cannot do this). They will have no circulatory system, so their respiratory rate will translate straight into metabolic rate. They will have no digestive system, so their ingestion rate will flow right into their metabolic rate. So it will just be 2 nodes feeding into 1 node, and progressively become a more complex tree as the creature evolves to become more complex.
  • It allows for simple life to never evolve some of these systems. A creature can ingest food via its skin, and respire via its skin. Therefore such a creature will never need to evolve a heart or a stomach or an intestine.
  • This will naturally produce a barrier for aquatic organisms to adapt to living on land, since living underwater will provide them with a constant flow of water and living on land will suddenly take that away. So creatures will have to evolve a means of finding and storing water on land if they want to survive there.
  • With this system in place, there are few other systems needed to implement all the remaining organ types. Reproductive organs are straightforward enough. Endocrinal organs will be a part of the Agent System. Integumentary Parts (skin, fur, scales, horns, spikes, shells) only confer bonuses to existing traits (physical defence, chemical defence, speed, etc.). Muscles and skeletons are also straightforward enough. It’s only really the Nervous organs and the Sensory organs that may need an extra system or two to give them purpose.


Here are examples of how the many planned organs (weird to say this for once instead of organelles) can have a use now with such a system:

  • Gill Slits: Increases ingestion rate of filter feeding while swimming by 50%. Increases respiration rate while swimming by 10%.
  • Gills: Increases respiration rate while swimming by 50%.
  • Blood: Enables Circulation Rate (base rate is 100). Increases Respiration Rate by 100%.
  • Aorta (Simple Heart): Increases Circulation Rate by 100%.
  • Gastrovascular Cavity (Simple Mouth/Stomach): Reduces Digestion Speed by 50%, but increases nutrients yielded by digestion by 100%.

Next Steps

  • If it’s agreed that such a system makes sense, I can document it on the wiki for future reference.
  • We can look at how the Microbe Stage should transition into this system. Perhaps we could make the traits in the Microbe Stage renamed to match these names to make it more of a seamless transition?

A great backbone to work with here, nice thinking! I believe this is just the right amount of complexity for managing an organism’s vital statistics without going overboard with the nitty gritty details. We just need to be careful about how we decide on implementing this, else many players may find themselves overwhelmed by it still. The key is in gradually introducing new elements, and allowing the player to run into them at their own pace. Luckily for us, this problem mostly solves itself.

Ingestion rate is self explanatory for the most part, and shouldn’t be hard for players to figure out. They can absorb microscopic prey and detritus as a basic filter feeder, or develop a proper mouth to eat more or larger prey.

Digestion is a stat players will already be familiar with from the microbe stage, so it shouldn’t really present any additional complexity, even when developing specialized organs for it.

Respiration will undoubtedly be the new osmoregulation that players will contend with as they grow bigger and more complex. They’ll now need to keep an eye on how much gases their processes require, and make sure they are able to meet the needs of their processes. We want to make sure that this is forgiving enough that players can comfortably experiment with straining their limits without going extinct immediately.

Circulation is a brand new concept that players will be presented with. I like to think of it as a progression gate like the nucleus as players will need to develop some form of it before they can become bigger or more complex. We need to make sure that players are easily able to understand what is required, and how to acquire it.

Hydration could be easily ignored, or really just packaged into respiration for the most part until the player begins to emerge from their aqueous origins. However; I recognize that the ability to separate salt from water is the defining difference between salt and freshwater species on Earth, so we need to decide on if we want to require players to develop these capabilities themselves and how in depth it will be, or just omit it for ease of understanding. I suppose we could package it as a salinity tolerance stat and leave it at that.

Respiration and hydration I feel are pretty easy to carry over from the simpler stages as we can easily tie it to the stats of cells; High compound absorption of tissues can tie into increased natural respiration and hydration intake, and be reduced by organism size. Meanwhile, the respiration requirement would scale with the amount of organelles that require gasses to function.

This gives new multicellular organisms a passive ability to survive as long as they stay under a certain size threshold. Thus species will need to develop proper respiratory and intake systems to increase the soft cap on organism scale, or otherwise maintain a slower respiration rate by relying less on aerobic processes.

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Was just thinking, such a system could actually be quite easy to display to the player. We could have a “Metabolism” tab in the Organism Editor, that shows what the organism depends on for survival. Then we could have little Metabolism Trees that show the different food, gasses, and fluids that the organism needs for different functions.

This was just a super quick mockup, but for example an oxygen breathing carnivore would have this as their tree. Eat meat, fat, and bones. Breathe oxygen. And drink water. And your body will slowly turn these into energy.

Then you can click on Growth to see what compounds your body uses to grow you (from childhood to adulthood). Typically these will be the exact same.

Other Metabolism trees could include Poison/Venom/Toxins, Electricity, Pheromones, etc. The game would basically add them in for whatever extra metabolic functions you have.

Based on what the cells of that organism evolved to eat in the Microbe Stage, these trees will reflect different combinations of compounds needed to eat, breathe, or drink.

Lastly, we could have an energy balance bar (perhaps at the top of this panel) to show how much energy is produced each second by this organism’s metabolism, and how much of that is being spent on maintaining different parts or activities. The Energy Balance Bar, like the ATP Balance Bar, assumes you have all raw materials available. Obviously, if one of these compounds runs out, your organism stops producing energy.

EDIT: I think visualizing it like this greatly helps to imagine how all these systems will work together and be presented to the player. I may go back and create a more detailed visual concept of what the Metabolism tab could look like to represent the Metabolic Rate System.

Okay, as I mentioned on Discord, here is my megapost to bring together all my concepts on the Metabolic Rate System, Organism Editor, and Organism Gameplay, and how they all tie together.


To recap, this all started because I was researching what organs evolve into what organs (like gills into lungs), and was assigning functions to some of these organs. I then realized it was hard to assign functions to any of the Circulatory, Digestive, or Respiratory organs because we have absolutely no idea how those systems will work, so here is a comprehensive concept.

I will go through the different aspects of the game, and explain how this system will look for each aspect.

Organism Editor

We’ll start with the Organism Editor.

Metabolism Tab

The Organism Editor will have a Metabolism tab. This tab will contain the organism’s Energy Balance Bar, and the organism’s Metabolism Trees.

Energy Balance Bar

The Energy Balance Bar will be identical to the ATP Balance Bar. It will show you your sources of energy and your sinks. Energy can be consumed by locomotion and other activities, but it can also be consumed by maintaining organs like a poison gland or gills or a complex brain. Having an Energy Balance Bar will maintain continuity with the ATP Balance Bar of the Microbe Stage and be one less feature the players will have to learn in this stage. I had not included a concept since this feature is self-explanatory.

Metabolic Processes

Below the Energy Balance Bar will be the Metabolic Processes section of the Metabolism Tab. These will show all of the metabolic processes the organism carries out.

Collapsed view of the Metabolic Processes

Every metabolic process will be classified as being for the purpose of Energy, Growth, Toxins, Pheromones, Electricity, or some other category. In the collapsed view above, we see all compounds your organism needs to produce that particular product (with ratios). In this case, the needed nutrients for this organism are meat, bone, fat, oxygen, and water. These are all used to produce energy. They are divided into solid, gaseous, and liquid compounds based on whether you must eat, breathe, or drink them (which ties into Hunger, Respiration, and Thirst, which I’ll discuss later).

Expanded view of the Metabolic Processes

In the expanded view, we see how many exact metabolic processes produce that product, and we see the exact ratios (with possible alternatives for any reagents). We even see the names of the metabolic processes, which carry over from the Microbe Stage. Note that the metabolic processes you evolve in the Microbe Stage will determine your metabolism once you are a macroscopic organism.

In this case we can see the organism consumes meat for a medium amount of energy, and fat for a large amount of energy. We can also see he has evolved to consume bones as well as a substitute for eating meat, which means his body can use either compound for “Protein Catabolism”.

Also note that the Eat/Breathe/Drink distinction allows for many different feeding types. Underwater creatures don’t need to drink. Plants mostly only need to breathe. Some animals may need to eat a lot and some very little. Some will need to eat extra compounds to produce energy because they have unique metabolisms.

So to summarize, the player should be able to fully understand how much energy they produce, and what they need to eat to get that energy, from looking at the Metabolism tab. They can also get extra information like what they need to eat to grow, produce poison, etc. Basically they now know what to eat and how much energy and growth and other results it brings them.

Organism Mode

Now on to gameplay.

Nutrient Panel

Organisms will have a Nutrient Panel just like how cells have the Compound Panel. It’s basically identical. Nutrient Panel is just a more accurate and less technical sounding word that players will be able to relate to better. By definition, anything that you eat for some metabolic process is a nutrient, so even iron and hydrogen sulphide can be nutrients.

Note that there are also separate Hunger, Respiration, and Thirst Bars, discussed below. These “Instinct Bars” are meant to show you an overview of how many nutrients you have left simply organized by solid, liquid, or gas, whereas the Nutrient Panel breaks it down to show how much of each specific nutrient compound you have stored.

Instinct Bars

The Instinct Bars refers to the bars in the bottom right corner of the screen that display the health and condition of your organism. In the Microbe Stage these were just Health and ATP. Here, they are different.

Health Bar

Here you see the overall health of your organism.

We could make it so that as an organism ages past adulthood, their maximum health slowly decreases (it would not count as damage).


Health can be reduced by Damage. Damage comes in several different types. Some already exist in the game, like Physical and Chemical:

  • Internal Damage: I was originally going to name this as Physiological Damage, but it was too similar to Physical Damage. Perhaps we could rename Physical Damage to Concussive Damage? Anyways, this refers to damage that you take from a lack of food, air, or fluids (AKA starvation, suffocation, or dehydration). The way a lack of any of these three would cause damage is that they would reduce or eliminate your energy production. And just like how in the Microbe Stage, a deficit in ATP production causes your health to slowly reduce, so too will an energy deficit here cause gradual damage. We could expand it a bit more if we wanted to, and make small energy deficits at first not damage you but just make you less efficient at doing things.
  • Physical Damage: Already exists in the Microbe Stage. In the Macroscopic Stages this will refer to damage from Slash (claws, talons), Blunt (clubs, tail swings, punches, kicks), Pierce (horns, teeth, tusks), or Grapple/Crush (jaws, arms/legs, tentacles). This can be discussed in different threads.
  • Chemical Damage: Can be discussed more in a different thread.
  • Electrical Damage: Can be discussed more in a different thread.
  • Environmental Damage: Damage from extreme Acidity, Temperature, Pressure, or Salinity. Can be discussed further in a different thread.

Energy Bar

When the bar is full, it means your organism is producing 100% of the energy it needs. Anything below that shows a deficiency, and you will receive penalties (and your health will decrease over time).

I suggest that we make organisms only produce as much energy as they need. So if their Energy Balance Bar has a surplus, they just naturally scale down their energy production to match their need. If we don’t do that (and keep it as it is currently in the Microbe Stage), we could simply have a full bar represent 100% or more energy production (compared to need).

As discussed above, if energy falls below 100% of the need, we could have it apply different negative modifiers, or slowly damage you, or some combination of effects.

Hunger Bar

The hunger bar shows how much food you have stored out of your total storage capacity. If you have fat reserves, a notch in the bar shows where your regular food storage ends and where your fat reserves begin. If you eat above that amount you start producing fat, instead of having the food go into storage (stomach or tissues).

Food is intaken via passive absorption or via active ingestion. For example, early life will be able to just swim through water and absorb the nutrients out of the water through their skin. However, more complex life will need to find a way to more actively predate, or to produce food themselves (plants). Food is stored in the tissues or in a specialized digestive tract.

There do not need to be any additional penalties to your Hunger/Food bar reaching zero, since it is already represented by your energy production falling/halting if you run out of food.

One last thing, this and the following two bars could perhaps be moved to a different part of the screen, because otherwise we would have five different bars in the bottom right corner.

Respiration Bar

The respiration bar shows how much gas you have remaining. The bar is full when your gas storage (or lungs) are full. Unlike the Microbe Stage, gas needs to be acquired, stored, and consumed.

Gasses are intaken via passive breathing, or via active breathing. For example, some underwater organisms need to swim to get air to flow through their gills and inhale it, which means they’ll eventually suffocate if they stop moving. Gas is stored in the tissues or in a specialized respiratory tract.

This bar will rarely drop. It will only drop if you are an aquatic organism taken out to land, or a terrestrial organism thrown underwater. It also reduces if you perform a lot of strenous activity at once and use up all of the gas you have in storage faster than you can inhale more. Therefore, respiration (as well as hunger and thirst) are all different components of how much stamina you have (how long you can maintain energy expensive activity).

Thirst Bar

Still not sure whether this bar should come third or second in the UI.

The Thirst bar is full when your fluid storage is full. This will mean it’ll almost always be full for Aquatic organisms, and only deplete for terrestrial or aerial organisms.

Fluids are intaken via passive absorption, or via drinking. It is stored in the tissues or in a specialized digestive tract.

Other Factors

Environmental factors like Temperature, Acidity, Pressure, Light/Radiation, Salinity could also be represented by bars, but I think that would clutter the UI far too much. Instead, I think these are better represented by notifications. If you are in a normal state for any of these, you receive no notifications. If you are trending towards an extreme for any of these, or are currently in an extreme state of any of these (for example a temperature outside of your tolerable range), you receive a notification on the side of the screen.


So what are the effects of choosing such a system for the Macroscopic Stages?


  • Digestive system organs now have a purpose: This now enables the organs of the digestive system to have useful effects. They can store foods that have been ingested but need to be digested. They can increase the amount digested per second, or increase the efficiency of digestion (so no nutrients are lost). Some organs can specifically be evolved to improve digestion of a specific compound (like the foregut for ruminants to eat grass).
  • Respiratory system organs now have a purpose: This now enables the organs of the respiratory system to have useful effects. They can increase the rate at which gasses are inhaled/exhaled. They can allow gasses to be stored up. They can increase the efficiency at which gas is extracted from your breath. They can enable passive or active respiration. They can enable breathing underwater or above water or both. They can enable holding your breath or breathing in low gas environments.
  • Circulatory system organs now have a purpose: This now enables the organs of the circulatory system to have useful effects. The whole system acts as a second bottleneck after respiration. It improves the efficiency of respiration and allows for larger organisms to get gasses from their skin/mouth deep into their tissues where they need it. It also means the circulatory and respiratory systems need to evolve in tandem (since circulation depends on respiration).
  • Organisms don’t need to evolve Digestive, Respiratory, or Circulatory systems, but it greatly helps them to do so (if they can manage the tradeoffs). This allows for both simple and complex life to exist.
  • Models many physiological states with one system: This system models hunger, thirst, respiration, fatigue from a lack of any of them, and death from a severe lack of any of them.
  • Easy to understand: I know I wrote a lot, but at the end of the day this is actually a relatively simple system. You have three bars to track; Hunger, Respiration, and Thirst. All three bars are very intuitive as these are instincts we have ourselves. There is a clear Metabolism tab in the Editor that shows you what you need to eat. And a deficit of any of these three bars causes you to have less energy and potentially die.

Next Steps

If we accept such a system, I can start updating the wiki with these concepts. There is not much more to do beyond that.

It may also prompt us to consider how the Microbe Stage can be designed, going forward, to have as much continuity as possible with this system.

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I’m focusing a bit on detailing the rough plans for our macroscopic editor and have revisited this thread. Upon review of this concept, I have a few thoughts.

I do think it’s a wonderful idea to have circulation, respiratory, and digestive rates determine metabolic rates, but I wonder if we can afford to simplify things a bit from the more elaborate model here. This is elaborate enough for me to read through and understand, so I worry it might be a lot for the player to deal with. Even if it starts simply and with few nodes, once those other nodes get involved, I can easily understand if a player completely loses track of things and gets intensely confused after making a simple mistake. It’s elaborate enough reading through it; imagine having to deal with various interconnected parts related to these stats!

Here is an alternative proposal I have based on the premises of this post which I think is a pretty intuitive carry-over from the Microbe Stage.


To survive, you need to make sure your metabolic rate meets (preferably exceeds) your basal metabolic costs, established by the anatomy of your organism. This is essentially the same as making sure you make enough ATP to meet your basal ATP cost in the Microbe Stage. Your metabolic rate is defined by three things: your respiration and digestive rates, which are modified by your circulation rate.

To review how things work in the real world (I needed this): your digestive rate influences both how efficiently nutrients are extracted from organic matter and how quickly this process happens. Nutrients are then delivered throughout the body to cells. Cells then breakdown these nutrients via respiration, which is where the respiration rate matters. The rate at which both nutrients and oxygen gets transported throughout your body is the circulatory rate.

So, the whole process essentially looks like this:

  1. Eat something to get organic material
  2. Digest that organic material into nutrients, then circulate those nutrients to cells across the body
  3. Respire oxygen/whatever and circulate that gas throughout the body. Some breakdown of nutrients can happen without oxygen, but the majority of energy is facilitated via aerobic respiration.
  4. Each cell then breaks down nutrients locally, using respiration to breakdown nutrients.

EDIT: I will say that metabolism, respiration, digestion, etc. are influenced by an immense amount of factors and details. The whole process is much, much, much more complicated than I let on here, worthy of a life’s work of research. This is just a very simple way for us to understand things that hopefully is correct (input from the theory team is welcomed, please!)


Digestive Rate = Digestion is essentially the process which converts organic material into nutrients. It is congruent to the conversion of organic material into resources in the Microbe Stage via lysosomes and such. There are two components of the digestion rate: efficiency (in terms of breaking down nutrients) and time (how quickly food is broken down). They have a positive relationship. An increase in digestion time means an increase in efficiency, while a decrease in digestion time means an decrease in efficiency. So, digesting something quickly means you have quicker access to nutrients, but are much less efficient in extracting nutrients.

Let’s say you are a high-speed predator. You don’t eat all the time, but when you do eat, you eat a lot, and you spend a lot of energy getting that food. You also maintain a lot of high-energy adaptations, such as fast-twitch muscles and an extensive respiratory system. Considering this, it would probably benefit you to breakdown food very quickly, even if it means a loss of efficiency. If you breakdown whatever food you got slowly, you might not have enough nutrients available to fuel the moments in which you burst for prey.

Let’s say you are a grazing gentle giant. You graze on a low-energy food source, so you need to eat all the time, and need to extract as many nutrients from this food source as possible. Considering that, it is worthwhile to have a slower digestive system. If you consume your food source quickly, you lose on nutrients, which- considering your low-energy food source in the first place - isn’t very beneficial in the grand scheme of things.

In Thrive

In Thrive, your digestive rate will determine how quickly your organism breaks down organic matter into nutrients. You can generally influence either the rate or efficiency of digestion to suit your playstyle, through means that I will propose in another post.

Respiration Rate = Oxygen is needed as a catalyst for cellular respiration, serving as a controlled explosion of energy. Cells convert whatever nutrients they receive locally, meaning they also need local availability of adequate oxygen. Though there is some exchange between the rate and efficiency of respiration, a lot more emphasis is placed on adaptations which influence the efficiency of respiration. A more efficient respiration rate allows a quicker breakdown of nutrients into readily accessible energy.

Organisms which require a rapid burst of energy or live in low-oxygen environments, such as high elevations or the deep oceans, generally require elevated respiration rates to support their lifestyle. However, there is a certain point where the marginal benefit of extra oxygen absorbed does not justify the marginal cost of additional metabolic costs. This is why you don’t see every single organism in high oxygen environments maintain a hyper-powered respiratory system. It also means that even in low oxygenic environments, there is only a certain amount of oxygen available to be extracted.

Here is some more reading on respiration rates and size: Oxygen Consumption in Relation to Body Size, Wave Exposure, and Cirral Beat Behavior in the Barnacle Balanus Glandula | Journal of Crustacean Biology | Oxford Academic

In Thrive

In Thrive, your respiration rate will influence how quickly your nutrients are broken down into energy/ATP. Various factors can influence respiration rate, including surface area and dedicated organs. Your respiration rate will ultimately be limited by the amount of available oxygen in your environment.

Circulation Rate = Your circulation rate is essentially how fast things that need to get somewhere go in the body. Everything from water concentration, to nutrient circulation, to respiration is heavily dependent on circulation. Most smaller or less complex organisms don’t necessarily need an elaborate or dedicated circulatory system - many jellyfish, for example, get enough circulation from their digestive system to support their (relatively) low energy lifestyle. However, as complexity and size increases, there is a greater need for a more high-powered circulatory system.

In Thrive

In Thrive, your circulatory rate will essentially act as a coefficient affecting either your digestive or respiration rates (or both, though some adaptations might focus more on a specific rate). This coefficient might be neglected at first, but as you get more complex, you will need to supplement your digestive and respiratory rates to meet increasing energy demands.


I don’t think we necessarily need to explicitly represent “ingestion rate” in Thrive, and I think we can afford to essentially lump that in with digestive rate (unless I am neglecting something). Instead, along that line of thought, the way we deal with adaptations surrounding the jaws/teeth/digestive enzymes can essentially be focused on determining how much organic matter you receive from your food items. So essentially, “ingestion percentage” might be a better way to think of things rather than “ingestion rate”.

Say you catch a prey item with 20 organic matter, 10 of it being contained within bones/a exoskeleton and 10 of it being flesh. If you don’t have specialized teeth/jaws, you might only be able to access the 10 flesh you ate. So you would only get 10 organic matter, while the other 10 is either wasted (poop!) or left on the carcass. This extends further on - certain plants require certain teeth or jaw structures as well, and digestive enzymes mind you!

Similarly, I don’t think we should necessarily think of hydration as a “rate” and rather as a resource, similar to how we treat other resources in game currently (if this is what is meant in the OP and I am just misunderstanding the term “rate”, forgive me). I guess a “rate” relevant to hydration is the rate at which you lose water, which I think is an important factor to represent when it comes to amphibians, fish, etc. Beyond that, “water storage” can be a possible factor, though I need to read up on that a bit more.


So in summary, this is how the process will look…

  1. Catch and eat your prey/food, which will become organic matter to be processed. The amount of organic matter extracted depends on how much organic matter is accessible to you, based on teeth/jaw structure and digestive enzymes (we should probably rename “organic matter” to be more neutral for the brief period in time where quirky diets might exist early on; it’s ingested matter currently, yes?).
  2. Ingested matter becomes nutrients dependent on your digestive rate, which is affected by your circulation rate.
  3. Nutrients turn into ATP/energy dependent on your respiration rate, which is affected by your circulation rate.

And that’s it. A pretty simple system if you ask me. If this is what was meant by the original concept, forgive me - I might not have grasped the entirety of it! If nothing else, this can help us understand how the macroscopic stage can look like in terms of stats and the process of getting energy relative to the Microbe Stage. It should be a pretty smooth turnover.

Also note that this opens up various adaptations we see in real life surrounding the process. What if you want to increase your “organic matter storage”? Get a big gut, like a lot of huge herbivores. What if you want to increase your “nutrient storage?” Put on some fat deposits. The list goes on.

Hopefully this is a robust concept that you guys can see through. I do think whatever model we use will essentially be dependent on the ideas established by NicktheNick’s posts in some way, so I am planning to use these terms in some future concepts I am writing up now. So stay tuned!


Something else I like about this system is it’s straightforward to add a bioavailability layer on top. Every food has a different level of bioavailability, which is how efficiently our bodies can extract nutrients from it. Now, this is partially determined by our digestive system, but the food itself affects it a lot. For example, cooking our food increases its bioavailability a ton, which is what gives us the energy needed to support our brains.

A system like that would allow us to emergently add benefits to stuff like fire, cooking, and food choice.


Yeah, that’s a very good point as well. Fibrous material like plants are generally less bioavailable than meat, so that goes to further point herbivorous animals to prefer a more efficient yet long-lasting digestion rather than a less efficient, faster digestion. For carnivorous organisms, there’s less of that pull since meat is more readily accessible.

I think additional stuff should also depend on these rates as well, so one might actually have a reason to take it further than the rest of them. For example, circulation limiting body size, and maybe making you more susceptible to poison.

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I have been reading the thread for a while now and overall the idea is fantastic.There are some sentences that I’m not understanding very well or aren’t written with the most scientificly correct terminology. I think overall it’s clear what the idea is, though I will try to correct/pinpoint some sentences.

This is written vaguely, respiration exclusively converts glucolitic metabolites and derivates into CO2 generating a potential capable of reconverting ADP into ATP, but the whole process of breaking down e.g. Proteins and Polysaccharides into amino acids and simple sugars, respectively, involves quite a lot of metabolic paths and not only respiration. Probably a better idea would be that nutrients are fully oxidized, wether it is by aerobic respiration or any other metabolic pathway. I know you want to keep it simple and straight to the point.

Yeap, here comes the concept of Lactic Acid and the balance between aerobic respiration and lactic fermentation. I don’t know if you are familiar with these 15.3: Lactic Acid Fermentation - Chemistry LibreTexts (the next step would be the Cori cycle Cori cycle - Wikipedia, which I already commented here New organelle for storing ATP as glucose as Gluconeogenesis - ATP usage to glucose recovery - is strongly related to the Lactic Acid Fermentation, through the Cori cycle). So really nice idea there.

Yeap, keeping it simple without losing scientific accuracy.

Again here you take into account only the aerobic respiration and usage of O2 as electron acceptor (maybe I got a bit technical here :sweat_smile:), and, even though as we know today all eukaryotic/large organisms use aerobic respiration we can’t know what would evolution bring out in another planet.

Pretty cool, though this probably will arise naturally once the ATP consumption is balanced and proportional to the number of cells/mass.

A lot of oxygen does not necessarily translate into a quicker respiration. And there are problems when respirating too much, during the 80’s the leading theory about why do we age was that too much oxygen destroyed our cells and it is partially true, so … yeap, too much oxygen is not necessarily beneficial either. I would say that the oxygen avaliability is a crucial factor to the organism’s size/mass.

Yeap pretty much it, nice :blush:

I’d reccomend to take a look to Camel’s blood cells Blood Cells Protect From Dehydration — Biological Strategy — AskNature and Kleiber’s paradox (now law) Kleiber's law - Wikipedia.



Well, I hope the feedback is useful :slight_smile:, feel free to ask/comment me anything.


Thank you very much for the feedback!

Yeah, my understanding of the metabolic processes related to proteins and polysaccharides isn’t very deep. I am also wary of having that much for the player to worry about when it comes to how they digest things, since I am sure the “traditional” process of digestion and cellular respiration can be tricky enough to grasp. Perhaps we can accommodate that level of detail simply enough in a concept for organ systems.

I am vaguely familiar with lactic acid fermentation. I see it becoming pretty relevant when we discuss the idea of stamina, where the rate at which your stamina declines can be relevant to an adaptation meant to approximate the Cori cycle and lactic acid fermentation.

Yes, I am currently taking into account aerobic respiration because I honestly have very little awareness of how other, more exotic forms of respiration would work :sweat_smile: I also am not taking into account more anaerobic means of respiration that we know exist I realize. I think it is important to make sure the player isn’t confused with our most fundamental system in the macroscopic stage by introducing too many factors, but again, I do think things like that could be introduced in the future when we discuss things like stamina.

Interesting! I think it would be best if we simulate this by having reduced and varying marginal benefits of enhancing your respiratory system. For example, a 10th upgrade to your respiratory system might benefit a large organism pretty well, but that same 10th upgrade to your respiratory system might not be as necessary for a small organism; and for both organisms, the 10th upgrade doesn’t have as much of a benefit as the 1st respiratory upgrade did. Would that be a decent representation of this fact? I worry about making the player have to balance their respiratory system between “too much respiration” and “not enough respiration” (that could be a very cool mechanic to consider later, but for now, I just want a rough idea of everything).

If you don’t mind, I would like to contact you and ask about this more when I start fleshing out a proposal for how we will deal with various organ systems in the macroscopic stages. I understand the basic description of Kleiber’s paradox, but I would like to understand it more to help us understand how we can utilize circulatory systems engagingly in the future as a way to address size.

Thank you again for your feedback!


Yeap that’s the thing, before cellular respiration (taking that as the preferred metabolism) nutrients have to be broken down, so in order to keep it simple and clear to the player we could combine the both to make the “full oxidation organ” that just generates (or regenerates) ATP. But yeah all digestion is just a process of oxidation, for example proteins are broken down into amino acids by oxidazing the peptide bond.

In a sentence: “It’s the metabolic process necessary to keep glycolysis working

I was just thinking about a player’s choice (although unlikely) not to build/have any aerobic respiration protein/organelle throughout the cellular stage, therefore at the macroscopic stage the species would not be able to do aerobic respiration.

Yeah that would do the job, though I must point out that the reactive oxygen species (ROS) are indeed a problem to consider; and too much total lung capacity (TLC - though the name would be change depending on the respiration organ’s name) leads to a lower lactic acid fermentation which ultimately leads into either a fat loss (that’d have tons of really bad physiological consequences) or a protein loss (that’d have physical consequences) as it happens with the sledge dogs, as they do not generate almost any lactic acid during physical exercise so they don’t feel tiredness at a point of oxidasing proteins to produce ATP. Maybe I got a little too far with the explanation, let me know if anything is not clear. I would also like to add that perixisomes exist hahaha.

Sure!! :smile:

Anything else don’t hesitate in contact me.

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